This invention relates to a lock having specially cooperative latch bolt and dead bolt mechanisms.
In recent years, the increased frequency of unauthorized entry has stimulated widespread usage of dead lock bolts arranged to supplement the customary latch bolt. In the simplest form of such an arrangement, the latch bolt and dead bolt are totally independent of each other. A separate inside turn operates the dead bolt, in addition to the inside knob or handle for the latch bolt. On the door exterior, an optional key actuator might be employed for the dead bolt, in addition to the outside knob actuator for the latch bolt. The outside knob may, if desired, also have a key lock. More recently, dead lock bolts of greater throw length are being substituted for the older shorter style, in efforts to frustrate improper entry through the technique of prying or otherwise damaging the door casing, as well as accommodating door frame warpage and the like.
These factors do offer a greater measure of security, but also involve greater complexity for those persons legitimately using the door, particularly under panic conditions. Hence, enlightened fire codes presently require installation of locks enabling both the latch bolt and the dead bolt to be rapidly retracted under panic conditions by operating just the inside knob. Presently marketed products achieve this by various ways of interconnecting the dead bolt mechanism with the latch bolt mechanism. Some of these products do in fact effect an excellent panic exit feature, but in doing so present other problems. One such problem involves "handing". Another significant problem involves tampering with the lock.
As to the feature of handing, a "handed" lock is one which can potentially be employed in a left-hand or a right-hand door arrangement by rearranging the interrelationship of some of the internal components of the lock. Presently, for those locks which cannot be so handed, two separate models must be manufactured and inventoried throughout the trade. There are locks on the market capable of handing. Unfortunately, although some can be handed by specially trained personnel in the field, the better known locks must be handed by trained personnel at the factory, or by a locksmith. And, since locks typically are installed by carpenters or other building tradesmen with no special locksmith training, even the partial disassembly and reassembly of the intricate components by such personnel to "hand" the lock results in a maximum of frustration, limited success, and added expense. The alternate choice of engaging a locksmith also adds considerable expense.
As to the tampering problem, the difficulty primarily arises with interconnection of the dead bolt mechanism to the latch bolt mechanism to provide the panic exit feature. This interconnection can enable the dead bolt to be thrown back by unauthorized tampering with the latch bolt mechanism particularly the spindle, from the outside. This can be done by forced removal of the outside knob with a hammer or other tool, and rotation of the exposed spindle with pliers or the like.